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1. Overview of Pharmaceutical Plastic Packaging Materials
1.1 Definition of Pharmaceutical Plastic Packaging Materials
Plastics are collectively referred to as polymeric materials with high plasticity. They are mainly composed of resins and various chemical additives and represent one of the principal materials used in pharmaceutical packaging. Compared with glass packaging, plastic packaging materials are lightweight, exhibit high mechanical performance, possess good corrosion resistance, are easy to seal, and are relatively low in cost. In recent years, they have been widely used in pharmaceutical packaging applications.
1.2 Characteristics of Pharmaceutical Plastic Packaging Materials
(1) Good mechanical performance. Plastics exhibit favorable strength and elasticity, with resistance to bending, impact, and compression. They are also abrasion-resistant and not prone to breakage.
(2) Good chemical stability. Compared with the susceptibility of glass packaging to hydrolysis and the tendency of metal packaging to corrode, plastic packaging materials show superior chemical stability. They are resistant to common acids, alkalis, and salts, and demonstrate excellent resistance to chemical media such as oxygen, moisture, and carbon dioxide present in the external environment.
(3) Lightweight nature. Plastic packaging materials are relatively light due to their low density, which is approximately half that of glass and about one-fifth that of metals.
(4) Excellent processability. Plastics are thermally sensitive and highly moldable, making them suitable for forming, heat sealing, and lamination, as well as convenient for printing and decoration.
(5) Good optical properties. Plastic packaging materials can be manufactured to be transparent or opaque depending on the photosensitivity of the drug.
(6) Low cost. Plastic packaging materials are relatively inexpensive, and their low weight also reduces transportation costs.
2. Types of Pharmaceutical Plastic Packaging Materials and Their Advantages and Disadvantages
2.1 Polyethylene (PE)
Polyethylene, abbreviated as PE, can be classified according to density and molecular structure into linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). Different densities of polyethylene exhibits different properties.
HDPE is relatively rigid and tough, shows strong resistance to a wide variety of chemicals, has relatively low transparency, and offers good barrier properties.
LDPE is soft and transparent, with excellent heat-sealing properties; however, it has poor barrier performance against gases and odors.
LLDPE exhibits better toughness, elasticity, and barrier performance than LDPE. It can be produced in thinner films—approximately 20% thinner than LDPE—resulting in softer and thinner films with good heat-sealing properties.
2.2 Polypropylene (PP)
Polypropylene is a polymer of propylene. Its is similar to polyethylene, but it has a lower density and appearance is lighter, making it the lightest among commonly used plastic packaging materials. Polypropylene possesses high chemical resistance and superior mechanical properties compared with PE, particularly excellent flexural resistance and rigidity. It also has higher transparency than PE.
PP offers good moisture resistance and better gas barrier properties than PE, effectively preventing odor transmission. It has good heat resistance, can withstand boiling water, and is suitable for packaging products that require high-temperature sterilization. It is non-toxic and odorless.
However, polypropylene becomes brittle at low temperatures, showing much poorer cold resistance than PE, which limits its use in low-temperature conditions. Its aging resistance is relatively weak, often requiring the addition of antioxidants, and its printability is poor.
2.3 Polyvinyl Chloride (PVC)
Polyvinyl chloride is produced by polymerization of vinyl chloride monomer. It is widely used in the packaging of solid dosage forms. Currently, a large number of aluminum–plastic blister packs for tablets and capsules are made of PVC.
PVC materials offer good transparency, high strength, and excellent printability, meeting the requirements for moisture resistance, microbial protection, and anti-fogging in tablets, capsules, and traditional Chinese medicine preparations.
PVC itself is non-toxic; however, vinyl chloride monomer is hepatocarcinogenic. Therefore, when used for pharmaceutical packaging, the residual monomer content in PVC sheets must be strictly controlled to within one part per million. In addition, PVC has relatively poor heat resistance and is prone to deformation when heated. Stabilizers and plasticizers are often added to reduce processing temperature and adjust hardness. Pharmaceutical-grade PVC sheets should use non-toxic additives.
2.4 Polyvinylidene Chloride (PVDC)
Polyvinylidene chloride is formed by copolymerization of vinylidene chloride (VDC) and vinyl chloride (VC). PVDC exhibits good printability, acceptable transparency, excellent heat-sealing properties, and chemical resistance. Its most outstanding feature is its extremely low water vapor and oxygen permeability, making it an excellent high-barrier material.
However, PVDC also has disadvantages, including poorer thermal stability and aging resistance compared with PVC. Residual vinylidene chloride monomer is toxic and may pose teratogenic and carcinogenic risks upon long-term exposure. Therefore, strict control is required when used for pharmaceutical packaging, with residual monomer content not exceeding three parts per million.
Compared with PE and PP, PVDC is relatively expensive. In pharmaceutical packaging, it is mainly used in combination with PE or PP to form composite films, thereby improving airtightness and barrier performance, and enhancing moisture resistance, oxygen barrier properties, and sealing performance.
2.5 Polyester (PET)
Polyesters are polymers containing ester bonds; in pharmaceutical plastic packaging materials, polyethylene terephthalate (PET) is most commonly used. PET exhibits excellent mechanical properties and the highest toughness among commonly used thermoplastic materials.
It has high tensile and impact strength, with film tensile strength comparable to aluminum foil and impact strength three to five times higher than that of ordinary films. It offers good flex resistance but poor tear strength. PET also shows good resistance to both low and high temperatures, as well as favorable chemical resistance, though it is not resistant to strong acids or strong alkalis.
Its gas barrier performance is relatively good and is considered medium-level. PET is non-toxic, odorless, and safe, with high transparency and gloss, and it provides good shielding against ultraviolet radiation.
However, PET has poor heat resistance, is prone to degradation in hot water, cannot withstand high-temperature steam sterilization, tends to accumulate static electricity, and has poor heat-sealing properties.
3. Applications and Considerations for Pharmaceutical Plastic Packaging Materials
Plastics are easy to process and can be manufactured into plastic bottles and bags of various specifications and shapes. They can also be combined with other packaging materials to form high-performance composite packaging materials.
Pharmaceutical plastics are lightweight, strong, resistant to breakage, offer good sealing performance, moisture resistance, and hygiene, and can be used directly for drug packaging without cleaning or drying. They are therefore excellent pharmaceutical packaging containers, widely used in the packaging of oral solid dosage forms (such as tablets, granules, and capsules) and liquid preparations (such as syrups).
Despite their advantages, appropriate selection must be made according to the dosage form. For example, plastic bottles for solid drugs are usually made opaque by adding titanium dioxide or white masterbatch. For liquid drugs or those requiring transparency, amber or other colored masterbatches are often added to provide sufficient transparency while also blocking sunlight.
Due to the inherent properties of plastics, their barrier performance is relatively limited. If the product contains volatile components, these may permeate through the container wall, leading to loss. In addition, various additives—such as plasticizers, light stabilizers, heat stabilizers, lubricants, antioxidants, colorants, and antistatic agents—may be incorporated during production. Care must be taken to ensure that these additives are compatible with the drug and do not pose toxicity or irritation risks.
4. Conclusion
A wide variety of plastic packaging materials are available and should be selected according to the specific characteristics of the drug. LDPE can be chosen for flexible packaging; HDPE and PP are suitable for drugs requiring good moisture resistance; drugs sensitive to oxygen should use high-barrier PVDC-based composite materials; and for oral liquid preparations, polyester packaging is an excellent alternative when glass bottles are not used.
Plastic infusion bags can rely on their own elasticity to deliver the solution without forming an air circuit thereby, avoiding secondary contamination associated with glass infusion bottles, and represent an effective replacement for traditional glass infusion containers.
